Lowly priced digital calipers have been available on the market for some years. Most of them are produced in China or the
Far East and possess a serial interface, over which measuring data can be
transferred to other devices. Despite their price ($10 - $20) these calipers
are very reliable and precise. Apart from the original use as calipers, they
can be used as position display or Digital Readout DRO for linear axles of
small machine tools in the same way as linear glass scales. For this purpose
digital scale readouts with mounting brackets are available in different
lengths. In small CNC machines these scales can serve as reference givers and
tool length givers. Even a 3D Digitizer / 3D Scanner for 3D measurements as well as
tensile tests can be easily implemented. A complete workshop can be digitized for little
money.

To use the measuring data (capturing, displaying, converting etc.), it is
necessary to connect the digital calipers to a PC using their serial interfaces.
For this purpose the interface and multiplexer Caliper2PC has
been developed and is described here (see video).

Within the scope of this project the hardware and software required to
equip the machines accordingly have been designed. The result is a
future-oriented, user-friendly and adaptable system which offers aside from the
numerous implemented features, space for own additions (API - software
interface).

fig. 2: Milling Machine
with Caliper2PC DRO X,Y,Z and glass scales.

fig. 3: Optimum
Lathe with Caliper2PC DRO and Touchscreen.

The communication between the multiplexer Caliper2PC and the host PC
occurs via USB. No external power supply is required, since the Caliper2PC is
power-supplied by USB from the host PC. The Caliper2PC offers on the input side
connections for up to 6 digital calipers. This way it is possible to connect, for
example, a milling machine (3 axes; x-, y-, and z-axis), a lathe (2 axes) and
an additional digital caliper for the QA (see fig. 1). To connect the digital
calipers to the Caliper2PC interface, a connecting lead must be attached (see
chapters "Pin Assignment" and "Retrofitting
Calipers").

All supported linear encoders can be used simultaniously (e.g. glass scales,
linear scales and Mitutoyo Digimatic devices).
The DROs can be reset to zero or to any given value in any position. For every linear encoder the
Caliper2PC interface offers an additional input port for an edge finder or to connect a
pedal switch to capture the momentary value for instance (see chapter "Retrofit with Capture Button"). Alternatively, reference switches or end switches
used with CNC machines can be connected to detect and process the switch
states. The Caliper2PC software can be used with a webcam as a video edge finder.

In addition, two tachometers are implemented in the Caliper2PC interface. This allows displaying and regulating tool
machines' spindle speeds.